1. Field of the Invention
This invention relates to a printing machine, and more particularly to a sound reducing apparatus for the printing machine.
2. Description of the Prior Art
Printers, copying machines, facsimile machines and so on are currently available as print producing machines.
Such a print producing machine includes a sheet inlet for feeding sheets thereinto and a sheet outlet for discharging printed sheets.
A sheet tray is disposed near the sheet inlet while a printed sheet tray is positioned near the sheet outlet.
Sheets are fed into the printing machine from the sheet tray via the sheet inlet, are printed, and are discharged via the sheet outlet onto the printed sheet tray. The sheet inlet and outlet are relatively large such that a maximum amount of sheets can be fed and discharged via them.
The printing machine also includes a number of devices such as motors, and units operated by the motors. These devices tend to generate operational sound or noise when they are in operation.
It is preferable to reduce sound or noise generated in the printing machine in order to protect the environment where the machine is installed. However, the printing machine tends to increase sound or noise, since it is required to perform its operation at an accelerated speed. For this purpose, driving mechanisms of the printing machine have to operate at high speeds, which causes generation of mechanical sound or noise.
In addition to the foregoing mechanical sound or noise, various kinds of sound or noise are also generated while sheets are being conveyed through the printing machine.
FIG. 42 to FIG. 46 of the accompanying drawings are schematic views showing a sheet feeding mechanism in a printing machine. Referring to FIG. 42, the printing machine includes a printing drum 1 on which a stencil is wound. The stencil is perforated in accordance with an original image. The image is printed on a sheet 32 with ink oozing from the printing drum 1 via the stencil.
The sheet 32 is brought into pressure contact with a surface of the printing drum 1 by a press roller 3 such that ink will be easily transferred onto the sheet 32. For this purpose, the press roller 3 is swung toward the printing drum 1 while the sheet 32 is in contact with the printing drum 1. As the sheet 32 is separated from the printing drum 1, the pressure roller 3 is swung back from the printing drum 1. No ink oozes from the printing drum 1 while the pressure roller 3 stays away from the printing drum 1.
Referring to FIG. 42 again, the sheet 32 is paid out from a sheet cassette by a sheet feeder 93. The sheet feeder 93 is positioned above a sheet cassette, and includes a sheet feed roller 9 and a pick-up roller 10. The sheet feed roller 9 feeds the top sheet 32 in cooperation with a separating roller 8.
A sheet separating claw 16 and a conveyer belt 15 are located at a position which is near the printing drum 1 and opposite to the sheet feeder 93, i.e. downstream of the press roller 3. The sheet 32 separated from the printing drum 1 by the sheet separating claw 16 is conveyed by the conveyer belt 15 toward the sheet outlet. The sheet separating claw 16 blows air into a space between the printing drum 1 and the sheet 32, thereby stripping the sheet 32 from the surface of the printing drum 1.
With the foregoing sheet feeding mechanism, sound or noise is generally generated in the following cases or areas.
(1) When a leading edge of the sheet 32 strikes a nip between a pair of register rollers 6, the sheet 32 vibrates and makes sound (as shown by (a) in FIG. 42). PA1 (2) When the register rollers 6 rotate in response to the rotation of the printing drum 1 but when the sheet feed roller 9 remains stationary, the sheet 32 is curved as shown in FIG. 43 and is then returned to its original state by tension applied thereto, generating a hissing sound (as shown by (b) in FIG. 44). PA1 (3) The press roller 3 generates sound when it strikes the printing drum 1 (as shown by (c) in FIG. 45). PA1 (4) The air from the sheet separating claw 16 makes a hissing sound (as shown by (d) in FIG. 46). PA1 (5) A power transmitting mechanism also generates sound when gears come in and out of contact with their mating gears, or cams and cam followers generate slip noise during their intermittent engagement.
The hissing sound caused by the sheet in items (1) and by the sheet feeding mechanism (2) accounts for approximately 40% of the total amount of sound. Next comes the sound in item (4) and (3).
To reduce or suppress the generation of the foregoing kinds of sound, the following countermeasures are conceivable: (i) to reduce the sound generating sources; (ii) to provide vibration damping mechanisms; (iii) to provide vibration controlling mechanisms; (iv) to provide sound reducing mechanisms; and (v) to provide anti-air-vibration mechanisms.
The countermeasure (i) is most effective of all. Specifically, this countermeasure is performed by: (a) reducing a speed, at which the sheet 32 comes into contact with the register rollers 6, to a minimum range where the printing operation is allowable; (b) gently tensing the sheet 32 at a reduced speed; (c) reducing energy with which the press roller 3 is brought into contact with the printing drum 1; (d) using a belt reduction system in place of a gear reduction system; and (e) using sound reducing materials.
However, it is still difficult for the foregoing countermeasures to completely reduce sound and noise. This is because the printer has a number of openings through which sound or noise leaks outward. As described above, the printing machine has the sheet inlet and outlet, which are essential not only for feeding and discharging the sheets but also for performing maintenance work, removal of jammed sheets, and so on. Since these openings cannot be closed or sealed, sound in the printing machine tends to leak out via them.
Japanese Utility Model Laid-Open Publication No. Hei 3-093,130 proposes a sound reducing apparatus for preventing leakage of sound via a sheet inlet and a sheet outlet. The sound reducing apparatus comprises a sheet-feed-sound reducing unit and a sheet-discharge-sound reducing unit. The sheet-feed-sound reducing unit includes a stationary cover attached to a printing machine frame under a feed tray, and a movable cover supported on a support shaft of the stationary cover. The movable cover is opened and closed. The sheet-discharge-sound reducing unit is structured similarly to the sheet-feed-sound reducing unit, and includes a stationary cover and a movable cover.
A sheet cassette having a sound reducing cover is proposed in Japanese Utility Model Publication No. Hei 5-012,183. This cover is intended to reduce the size of a sheet inlet.
Japanese Patent Laid-Open Publication No. Sho 60-093,047 proposes sheet cassettes, each of which has a sound-reducing cover.
The sound reducing mechanisms proposed in the foregoing publications seem to have the following problems. Although leakage of sound from the printing machine can be prevented by closing or sealing the openings using sound reducing members, the printing machine itself tends to become large in size and complicated in structure. Further, it becomes difficult to load or unload the sheets into or out of the printing machine. Further, there is a new problem that the printing machine requires a large vacant space around it so as to be opened and closed.
If the sheet inlet is down-sized for the purpose of sound reduction, curled or wrinkled sheets will not be fed reliably. Therefore, it is not preferable to down-size the openings or spaces around a sheet feed path without due consideration.
Further, the sheet inlet has to be large enough to allow the movement of a sheet tray on which sheets are stacked. Therefore, the larger the sheet inlet, the larger the sound reducing cover. Therefore, a large space is required to open and close the sound reducing cover.
When each sheet cassette or sheet tray has its own sound-reducing cover, the number of components will be increased, which will make the printing machine expensive.